The present invention relates to an etching chamber and a method for etching substrates and for cleaning and conditioning the surfaces of the chamber.
In the manufacture of integrated circuits, silicon dioxide, polysilicon, tungsten silicide, and metal layers on a substrate, are etched in predefined patterns to form gates, vias, contact holes, or interconnect lines. In the etching process, a patterned mask layer, such as an oxide hard mask or a photoresist layer, is formed on the substrate using conventional photolithographic methods, and the exposed portions of the substrate are etched by capacitive or inductively coupled plasmas. Commonly used etchant halogen gases include fluorinated gases such as CF4, SF6, and NF3; chlorinated gases such as Cl2, CCl4, SiCl4, and BCl3; and brominated gases such as HBr, Br, and CH3Br.
In the etching process, the etching chamber is contaminated by a thin etch residue layer that deposits on the walls and other components in the chamber. The composition of the etch residue layer depends upon the etchant gases, the material being etched, and the composition of the mask layer applied to the substrate. When silicon is etched, silicon-containing gaseous species vaporized or sputtered from the substrate are present in the chamber environment; and when metal species are etched, metal ions are present in the chamber environment. The resist or mask layer on the substrate is also partially etched away by the etchant gas to form gaseous hydrocarbon or oxygen species in the chamber. These different species combine within the chamber environment to form polymeric byproducts containing hydrocarbons, elemental silicon or metal species, and often also contain oxygen, nitrogen or boron. The polymeric byproducts deposit as thin etch residue layers on the walls and components in the chamber. The composition of the etch residue layer can vary widely across the chamber depending upon the composition of the localized gaseous environment.
The non-homogeneous, etch residue layer formed in the etching process has to be periodically cleaned to prevent contamination of the substrate, and to provide internal chamber surfaces that have consistent and homogeneous chemical compositions and surface functionality, otherwise the etching processes performed in the chamber can varying widely in etching properties. In a traditional wet cleaning process, an operator periodically shuts down the etching machine, and uses an acid or solvent to scrub down the chamber walls. In the competitive semiconductor industry, the increased per substrate cost arising from downtime of the etching chamber, is undesirable. Also, because the wet cleaning process is manually performed by an operator, it often varies from one session to another, and limits the reproducibility of the etching process conducted in the chamber.
Another commonly used etch chamber cleaning method uses an insitu ionized plasma which is generated inside the etch chamber, to clean the chamber walls. However, the in-situ ionized plasma species are highly energetic and can rapidly erode the chamber walls and chamber components. It is expensive to periodically replace the eroded parts and components in the chamber. Also, surface erosion of the chamber surfaces and components by the energetic plasma species, can often result in the instability and lack of reproducibility of subsequent plasma etching process steps performed in the chamber. For example, variations in the concentration, type, or surface functional bonds or chemical groups on the exposed surfaces of the walls and components in the chamber, affect the sticking coefficient of gases and vapors on these surfaces, and consequently, the gaseous plasma etching chemistry in the chamber. Chamber surfaces having excessively active surface functional groups can deplete the concentration of gaseous chemical species needed to etch the substrate. Furthermore, the relatively high plasma power levels required to achieve acceptable cleaning rates tend to generate residue byproducts that damage system components and which cannot be removed except by physically wiping the internal surfaces of the chamber. For example, NF3 plasma used to clean aluminum chamber surfaces results in formation of AlxFy compounds that cannot be etched away by nonchemical processes. As another example, NF3 gas that is used to clean Si3N4 CVD deposition systems result in formation of NxHyFz compounds that are deposited on the exhaust or vacuum pump and affect the reliability of the exhaust pump.
In chemical vapor deposition (CVD) processes, cleaning gases that are activated by microwaves in a remote chamber and further energized by capacitive coupled plasmas in-situ in the CVD chamber, have been used to clean the relatively thick and homogeneous CVD deposit layers formed in these chambers. In a typical CVD process, reactive gases are used to deposit a layer of material, such as aluminum or silicon dioxide, on the substrate. During the deposition process, the CVD deposits that are formed on the chamber walls and surfaces are often as thick as the CVD layers deposited on the substrate. The CVD deposits also have a relatively uniform and homogeneous chemical composition that corresponds to the material deposited on the substrate. The thick and chemically homogeneous CVD deposits can be cleaned by a high power microwave and capacitive coupled plasma, as for example, described in U.S. Pat. No. 5,449,411, which is incorporated herein by reference. In another example, commonly assigned European Patent No. 555 546 A1 discloses a process for CVD of silicon and removal of silicon deposits from the walls of the CVD chamber using a microwave plasma of NF3 or CF4/O2. Similarly, German Patent No. 4,132,559 A1 also describes a method of cleaning a CVD deposition chamber using a remotely generated microwave plasma of NF3.
However, the CVD chamber cleaning processes for cleaning thick and stoichiometrically homogeneous CVD deposits in deposition chambers are not suitable for cleaning the thin, variable composition, etch residue layers formed on the inner surfaces of etching chambers. The thin etch residue layers make it difficult to stop the cleaning process, after removal of the residue layer, resulting in extensive erosion of the underlying chamber surfaces. Also, the variable chemical stoichiometry and composition of the etch residue layers at different portions of the chamber make it difficult to clean all of the residue. For example, the etch residue formed near the chamber inlet or exhaust is often thinner and has a higher concentration of etchant gas species (or of material being etched) than etch residue formed near the substrate which typically contains a higher concentration of polymeric or oxide mask species. It is extremely difficult to generate a plasma or gas that uniformly etches away the variable stoichiometric composition etch residue without either eroding the chamber walls below the thin soft residue layers, or conversely, failing to clean-off thick and chemically hard residue layers. For these reasons, known methods of cleaning CVD deposits in deposition chambers are ineffective at cleaning the ultra thin and compositional variant etch residue layers formed on the walls and components of etching chamber without damaging or eroding the underlying walls and component surfaces.
Thus, it is desirable to have a treatment process that maximizes the chemical reactivity of the cleaning gas to etchant deposits in an etching chamber and that minimizes the chemical reactivity of the cleaning gas to the exposed surfaces in the chamber. It is further desirable to have a method for treating the etching chamber that removes chemically adhered etchant deposits from chemically active surfaces in the chamber and restores the original chemical reactivity and surface functional groups of these surfaces. It is further desirable for the chamber cleaning process to remove etch residues having variable thickness and non-uniform chemical stoichiometry, without excessive erosion of the chamber walls and components.
The present invention provides an apparatus and method of etching a substrate in an etching chamber, cleaning a non-homogeneous, variable composition, etch residue layer from the walls and components of an etching chamber, and treating and conditioning ceramic surfaces in the chamber to provide highly consistent and reproducible etching performance. In the etching step, a substrate is etched in the etching chamber thereby depositing a thin etch residue layer on the surfaces of the walls and components in the etching chamber. In the cleaning step, cleaning gas is activated in a remote chamber adjacent to the etching chamber, for example, by applying microwave or RF energy in the remote chamber. The activated cleaning gas is introduced into the etching chamber to clean the etch residue on the walls and components of the etching chamber. It has been discovered that this method is particularly useful for cleaning etch residue strongly adhered to, or chemically reacted with, ceramic surfaces comprising aluminum nitride, boron carbide, boron nitride, diamond, silicon oxide, silicon carbide, silicon nitride, titanium oxide, titanium carbide, yttrium oxide, zirconium oxide, or mixtures thereof.
When etching certain materials, for example, silicon-containing layers, a relatively thin etch residue layer containing primarily polymeric, oxygen, and silicon-containing species, and having a thickness of about 0.01 to about 1 micron is formed on the chamber walls and surfaces. It has been discovered that such an etchant layer can be efficiently removed by a high flow rate, short burst of activated cleaning gas introduced into the etching chamber at a flow rate FR equivalent to a rate of about 200 to about 2000 sccm for a chamber having a volume of about 40,000 cm3 for a time period of about 0.5 to about 100 seconds to clean the etch residue, substantially without eroding the walls and components in the chamber.
Preferably, the cleaning process is performed while or immediately after, the substrate is being transported out of the etching chamber, to increase throughput from the etching chamber. Preferably, a short burst of a high flow rate of activated cleaning gas is introduced into the etching chamber for a short time period, while substrate is being transported in or out of the chamber, to clean and condition the surfaces in the chamber without eroding chamber surfaces or substrate surfaces. Another substrate is then transported into the chamber and the etching, transportation, and cleaning and conditioning steps are repeated, until the substrate supply is exhausted. In a preferred version, the remote chamber is maintained at a higher pressure than the etch chamber, to provide a more laminar flow of cleaning gas along the sidewalls and surfaces of the chamber.
It has further been discovered, in accordance with another aspect of the present invention, that superior cleaning and conditioning of etching chamber surfaces that are highly reactive to etch residue is achieved by introducing the activated gas into the chamber in multiple and discrete stages. The multicycle conditioning process comprises (i) a first stage, in which a first activated cleaning gas formed by maintaining the gas activator in the remote chamber at a first power level, is introduced into the etching chamber; and (ii) at least one second stage, in which a second activated cleaning gas formed by maintaining the gas activator in the remote chamber at a second power level different from the first power level, is introduced into the etching chamber. The cleaning gas in the first stage contains a more dissociated and chemically reactive species that removes the hard and thick etch residues at the chamber walls and components near the substrate. The cleaning gas in the second cleaning stage is activated at a lower power level to more gently treat and condition surfaces such as ceramic surfaces. The duration of each cleaning stage is from about 0.5 to about 100 seconds, and more preferably, from about 0.5 to about 94 seconds. The multicycle process can be repeated a sufficient number of times to treat the chamber walls and reduce the concentration of etch residue to the desirable level.
In yet another aspect, the present invention is to an etching apparatus comprises an etching chamber having a process gas inlet for introducing process gas into the chamber, a plasma generator for forming a plasma from the process gas for etching a substrate, and an exhaust system for exhausting the spent process gas from the etching chamber. A remote chamber adjacent to the etching chamber is used to generate an activated cleaning gas. A gas distribution system comprises (i) a gas conduit for transporting the activated cleaning gas from the remote chamber to the etching chamber, (ii) a gas flow distributor for directing the flow of activated cleaning gas substantially parallel, and adjacent to, one or more internal surfaces of the chamber, and (iii) a gas flow regulator for regulating the flow of activated cleaning gas into the gas flow distributor. Preferably, the gas flow distributor has nozzles positioned adjacent to surfaces in the chamber that have thicker etch residue layers, for directing the flow of activated cleaning gas to these regions to preferentially remove the thicker etch residue layers without eroding portions of the chamber having thinner etch residue layers.